BioSemi.nl

Posted here as this could be a hardware problem.

Dear Coen,

Please find depicted at the URL below a some curious artifact in our EEG, which we would very much appreciate if you could identify and suggest solutions.

http://i.imgur.com/2yMZT.png

The artifact looks like a very high amplitude pop, but at all electrodes on the scalp and around eyes. It occurred to me that the CMS-DRL could need some kind of descaling or extra salting, but it looks a dull silver like the rest of the pin electrodes.

Please do you recognise this artifact? The CMS-DRL socket on the ADC seems a little looser than on the other ADC. By trial and error, we remedied this problem in the past by suspending the electrode wires from a piece of string above the participant's head but they had to stay completely still in an awkward posture. This left us with unusable data. We haven't seen the problem for a while, after we instituted regular salting, but the problem now seems to have resurfaced, and perhaps salting is not relevant to the problem.

Any suggestions would be appreciated.

Best regards,

Tom

The Common Mode goes out of range for a short moment (blue light off). The system waits for approx 1 second before the measurement proceeds.

Reasons for CM to go out of range:

- CMS or DRL loosing contact with the skin
- Connection problem in wires/connectors CMS or DRL
- defect CMS active electrode
- Defect active electrode/wire/connector (other than CMS and DRL) safety circuitry is triggered.

Test the electrodes in water to find connection and wire problems and defect electrodes.

Salting is not relevant to this CM-out-of-range problem

Best regards, Coen (BioSem)

Dear Coen,

Thank you very much for your response. I found one defective flat active electrode. Removing the electrode from the system and replacing it with another active electrode seemed to correct the issue.

Best regards,
Tom.